1. Field of Invention
The invention relates generally to the field of non-destructive testing. More specifically, the present invention relates to a piezoelectric device that vibrates at an increased displacement amplitude.
2. Description of Prior Art
Wave motion through a medium can yield useful information about the medium without being invasive or damaging the medium; and may be remotely deployed to areas inaccessible by first hand observation. Examples of mediums through which wave motion is studied include liquids (subsea or downhole), sensors, load bearing structures, subterranean strata, and tubulars. Bonding between two or more members can also be evaluated by evaluating wave motion through a bond or interface of the two members. Devices used for generating waves include piezoelectric transducers, electro-magnetic acoustic transducers, wedge transducers, and the like.
Illustrated in FIG. 1 is an example of inducing and studying wave propagation within a hydrocarbon producing wellbore. Hydrocarbon producing wellbores 2 are drilled from the surface 16 into a subterranean formation 17 having entrained hydrocarbons. Typically set within the wellbore 2 is casing 4 bonded to the inner surface of the wellbore 2. The casing 4 is bonded within the wellbore 2 by cement 6 within an annulus between the casing 4 and wellbore 2. The resulting cement bond not only adheres the casing 4 within the wellbore 2, but also serves to isolate adjacent zones (Z1 and Z2) within the formation 17 from one another. Isolating adjacent zones can be important when one of the zones Z1, Z2 contains oil or gas and the other zone includes a non-hydrocarbon fluid such as water. Should the cement 6 surrounding the casing 4 be defective and fail to provide isolation of the adjacent zones, water or other undesirable fluid can migrate into the hydrocarbon producing zone thus diluting or contaminating the hydrocarbons within the producing zone.
To detect possible defective cement bonds, downhole tools 8 have been developed for acoustic interrogation within a wellbore 2. These downhole tools 8 are generally deployed on a wireline 10 into the wellbore 2. Typically, the wireline 10 inserts into the wellbore 2 through a wellhead assembly 11 via a pulley system 12. Wireline 10 is spooled on a surface truck 14 that can provide communication with the tool 8 through the wireline 10. Typically, transducers 18 are provided on the tool 8 capable for generating acoustic waves into the casing 4, and for recording the attenuation of acoustic waves as they travel, or propagate, across the surface of the casing 4. Each transducer 18 may only transmit an acoustic signal, may only receive an acoustic signal, or may both transmit an acoustic signal and receive a corresponding acoustic signal; where the corresponding acoustic signal propagates along and/or through the casing 4. Analyzing the propagation velocity and attenuation of the received acoustic wave yields information concerning the casing 4 or formation adjacent the wellbore 2. As is known, pads 19 can be attached to the outer surface of the downhole tool 8 that provide a pedestal on which the transducers 18 can be mounted.